The present invention relates generally to accumulating roller conveyors, and specifically to the provision of structure to minimize substantially the driving force applied to an article stopped with respect to the conveyor.
A typical prior art conveyor over which the present invention is an improvement is illustrated in U.S. Pat. No. 3,199,657 granted Aug. 10, 1965 to H. S. Harrison. That patent shows a conveyor formed of a plurality of conveyor rollers 30 mounted in slots 32 in a support plate 33, the slots 32 having a support surfaces 34 that are inclined upwardly and rearwardly with respect to the direction of travel of articles supported and conveyed by the rollers 30. The rollers 30 are contacted by a belt B which drives the rollers 30 in a direction to convey the supported articles in the direction indicated by the arrows. When the article being conveyed is stopped, the continued driving force of the belt B moves the rollers 30 upwardly along the support surfaces 34 to the left as viewed in FIG. 8 thereof so as to relieve the driving force applied between the belt B and the roller 30. This movement of the roller 30 up the inclined support surface 34 relieves the frictional drive of the belt B to about 10%, for example, of the weight of the article being conveyed. However, even with the driving force reduce only to 6% of its full driving value, this effect occurs beneath each article on the conveyor, whereby if there are ten hundred pound articles being accumulated, the driving force may be 60 lbs. total. The resultant driving force can crush fragile articles, or jackknife the loads, or if a roughened belt is employed at the end of the accumulating conveyor as a brake-type stop instead of an abutment as a positive stop, the driving force accumulated over several articles may overcome the braking action and cause the articles to travel further down the conveyor when they are supported to be stopped.
Another scheme for reducing the driving pressure between the conveyor rollers and the drive belt is illustrated in U.S. Pat. No. 4,109,782 granted Aug. 29, 1978 to I. Nakai. In this patent, the drive rollers 12 are mounted upon pivotal links 18 so that when an engaged article 36 is against the stop 40, the drive rollers 12 are pivoted in a clockwise direction about the pivot axis 38, thus to reduce the driving force transmitted by the drive rollers. This system also is subject to the same criticisms and objections as that discussed above with respect to the Harrison U.S. Pat. No. 3,199,657.
In U.S. Pat. No. 4,006,815 granted Feb. 8, 1977 to C. W. Werntz, an impositive drive or slip connection is provided between the drive for the conveyor rollers and the conveyor rollers. Such structures are objectionable in that a high degree of wear is encountered with a consequent requirement for continuous maintenance and replacement, as well as the fact that it is difficult to regulate the amount of slip and still insure good positive drive and good resumption of drive after a stopped article is released.
There have been provided heretofore accumulating conveyors wherein the drive belt driving the conveyor rollers has raised or thickened portions therein which serve to lift the conveyor rollers out of contact with the major portion of the drive belt when the conveyed article is stopped. Exemplars of such devices are illustrated in U.S. Pat. No. 3,650,376 granted Mar. 21, 1972 to W. J. Burgis, U.S. Pat. No. 3,730,330 granted May 1, 1973 to M. J. DeGood, and U.S. Pat. No. 3,958,684 granted May 25, 1976 to T. L. Garzelloni. Each of these devices is substantially more complicated than that of the present invention whereby to provide substantial maintenance and repair problems as well as lack of reliability in operation.
Even more complicated mechanisms have been provided in an effort to overcome the problems pointed out heretofore. Exemplars of such more complicated mechanisms are illustrated in U.S. Pat. No. 3,502,197 granted Mar. 24, 1970 to T. Kato et al., 3,716,129 granted Feb. 13, 1973 to A. C. Sadler, Jr., 3,810,538 granted May 14, 1974 to M. G. Moyes, 3,877,565 granted Apr. 15, 1975 to C. W. Werntz, and 3,905,470 granted Sept. 16, 1975 to R. Gebhardt. Each of these accumulating conveyors is so complicated that its reliability in operation is very low and maintenance and repair are excessive.